I have a few 73-77 Novas and you can certainly put an alarm on it. Some Nova's may not be worth much but some are worth a ton.
I would bury the siren up under the fender and there may already be some holes on the inner fender lip to use to attach the siren to the car. You may have to make a custom bracket to keep from drilling additional holes in the car. To get the siren wires into the car you should be able to use the existing grommet for the speedometer cable by the brake booster.
To add door lock actuators you will need to route wires from the side of the cowl between the door hinges and then also between the hinges on the door itself. If the car has original power windows, the conduit should be large enough to get the additional wiring from inside the car to inside the door but if not you would need to drill some holes, paint the bare edges of the steel and then install some rubber conduit tubes. These tubes could be purchased online or you might find a set off of a donor car from the same era in a salvage yard.
Here's the door jamb boots in my 77 Nova (might have to copy and past the link):
http://rides.webshots.com/photo/1111050427049730488JkjZoq
The doors should have factory pin switches in them but if not, new ones can be bought from Advanced auto or Autozone for a few bucks each. You do need to be aware that on the driver's door pin switch there are two wires going to it. The white wire is the dome light wire while the other is for the key buzzer. The white wire on this switch also goes to the passenger door switch (and the rear doors if it's a 4 door model). If there are no pin switches except in the driver's door then attach a section of 18 gauge white wire to the existing white wire already on the driver's door switch and then route this over to the other doors switches and connect them in.
If it's an automatic transmission car then there will be a large 12-14 gauge wire under the dash close to the column and this is the starter solenoid wire. By wiring in an alarm a relay on this wire it would keep the starter from engaging when the alarm is on. On a clutch car there should be a purple starter solenoid wire on the clutch pedal assembly.
Also present on the column should be a constant 12 volt wire and an ignition 12 volt wire. The factory wires are on an ignition switch assembly on the topside of the column. The flat connector on the bottom of the column is the turn signal and horn wires.
While mechanical hood locks are being installed less and less, you could also add this to the mix.
For the trunk pin switch to keep it out of the way, maybe have the plunger riding on the backside of the hinge close to the torsion rods that hold the trunk up. This way you won't have the switch hanging out close to the weatherstrip. This might take some creative brackets but the results will keep the switch well hidden and in a safe location to prevent damage to it.
For the parking lights, you can get this wire in the driver's door sill or at the headlight switch. I think it's a brown wire but be careful in the door sill as the tan is the sending unit wire for the gas gauge.
If you go to stevesnovasite.com/forums in the best of electrical there should be a wiring diagram for your car.
Jim
1968 Chevy II Nova Garage Find 2012
1973 Nova Custom
1974 Spirit of America Nova
1973 Nova Pro-Street